In the control of internal combustion engines, the conventional practice utilizes electronic control units having volatile and non-volatile memory, input and output driver circuitry, and a processor capable of executing a stored instruction set, to control the various functions of the engine and its associated systems. A particular electronic control unit communicates with numerous sensors, actuators, and other electronic control units to control various functions, which may include various aspects of fuel delivery, transmission control, sequential turbocharging system control, or many others.
A turbocharger consists of a turbine and a compressor. The pressure of the engine exhaust gases causes the turbine to spin. The turbine drives the compressor, which is typically mounted on the same shaft. The spinning compressor creates turbo boost pressure which develops increased power during combustion. A wastegate at the turbine intake limits the amount of boost pressure to protect the turbocharger and engine components. When boost pressure reaches a predetermined value, the wastegate opens to provide a bypass for a portion of the exhaust gases which pass directly into the exhaust manifold.
In a sequential turbocharging system, a plurality of turbochargers are provided. The engine controller activates the turbochargers as needed based on engine operating conditions. One form of a sequential turbocharging system is the dual turbocharging system in which a primary turbocharger is always active, and in which a secondary turbocharger is selectively activated by the engine controller, as needed.
One use for dual sequential turbocharging systems is on marine engines. Although existing sequential turbocharging systems, including dual type sequential turbocharging systems have been used in many applications that have been commercially successful, the existing systems do have some disadvantages. On very heavy boats, such as sport-fishing, where there is a significant amount of load on engines during acceleration, switching from single turbo mode to dual turbo mode may sometimes overload the engine from which it cannot recover. The engine must then switch back into single turbo mode to rebuild its boost pressure and accelerate. This overloading upon switching to dual turbo mode from single turbo mode may happen several times before the system finally may remain in dual turbo mode.